1. Field of the Invention
This invention relates to a novel optically active compound and a liquid crystal composition containing the same. More particularly it relates to an optically active compound having a similar structure to those of liquid crystal compounds and a chiral liquid crystal composition containing the same.
2. Description of the Related Art
At present, TN (Twisted Nematic) type display mode has been most broadly employed, but it is inferior in the response rate to emissive type display elements (electroluminescence, plasma display, etc.), and various improvements in this respect have been attempted. However, it does not appear that there is much possibility remaining for improvement to a large extent. Thus, various liquid crystal devices based on another principle in place of that of TN type display element have been attempted, and among these, there is a display method using ferroelectric liquid crystals (N.A. Clark et al, Applied Phys. lett., 36, 899 (1980)). This mode utilizes ferroelectric liquid crystal chiral smectic C phase (hereinafter abbreviated to SC* phase) or other chiral smectic phases such as SH* phase, SF* phase, SG* phase, etc., and the mode has the following three superior specific features as compared with TN type display mode:
a first specific feature consists in that it has a very high response rate amounting to 100 times the response rate of TN type display element; a second specific feature consists in that it has a memory effect to make the multiplex drive easy in combination with the above-mentioned high response rate; and a third specific feature consists in that the gray scale can be more easily obtained, only by controlling the inversion time of its polarity, as compared with TN type display mode, and hence it has been said that the mode is suitable for graphic display. PA1 an optically active compound expressed by the formula ##STR4## wherein R.sup.1 represents an alkyl group or alkoxy group each of 1 to 20 carbon atoms, hydrogen atom, a halogen atom or cyano group; ##STR5## and ##STR6## each represent ##STR7## wherein X represents hydrogen atom, a halogen atom or cyano group; R.sup.2 represents an alkyl group of 1 to 20 carbon atoms; the asterisk designates an asymmetric carbon atom; and m and n each represent 0 or 1, and a chiral liquid crystal composition containing the same.
However, in spite of its superior features, as to ferroelectric liquid crystals and compositions currently known, no sufficiently satisfactory results in the aspect of response rate have yet been obtained; thus it appears that this mode has reached a deadlock in terms of its practical aspect use. The reason is considered to be due to the fact that development of a liquid crystal compound having a very high response rate has not been realized.